Hugh Hefner‘s wedding to Crystal Harris was called off after she secretly planned to ditch the Playboy mogul at the altar in return for a $500,000 media deal, Page Six has exclusively learned.

Harris, 25, was shopping for a big-bucks deal to tell all after she ditched hapless Hef, 85, in front of 300 guests at their wedding at the Playboy Mansion on Saturday, to be filmed for a Lifetime TV special.

Yesterday it emerged that the pair had called off the wedding following an argument on Sunday, and the blond bride-no-longer-to-be immediately moved out of the mansion.

Harris had reportedly been secretly seeing Dr. Phil McGraw‘s son, Jordan, for months behind Hef’s back. Jordan is her songwriting partner, and they were seen cozying up at the Chateau Marmont in March.

A source told us, “Crystal wanted to ditch Hef at the altar. Her plan was to walk up the aisle and say she couldn’t go through with it. The wedding was to be filmed for a reality special, and her refusal to marry him would be a sensation. She was looking for a tie-in deal of around $500,000 for the exclusive ‘I ditched Hef at the altar’ interview. While there was interest, Crystal didn’t get an offer anywhere near half a million.”

The former Playmate started dating Hefner in January 2009, and they got engaged last December. It is not known if the Sunday argument was sparked by Hef finding out about her plan to humiliate him. But Harris’ manager, Michael Blakey, told us reports about her cheating with Jordan were “absolutely incorrect” and “total fiction.”

Of her plan to ditch Hef in return for a lucrative media deal, Blakey said that was “not true, to my knowledge.” He said of their split: “I have no idea what happened. All I know is that it was an amicable breakup.”

The cancellation is unfortunate timing for Playboy: Its July issue hits newsstands Friday, with Crystal on the cover. The coverline, according to sources, is “America’s Princess: Introducing Mrs. Crystal Hefner.”

Playboy reps didn’t get back to us. But Hef tweeted, “The wedding is off. Crystal has had a change of heart.” Will he ever find true love?